Water, employed in production processes such as a toner production process, a paper bleaching process, or a textile material dying process, is often colored. Even though COD and BOD, representing environment load, of such colored aqueous effluent are each regulated to be the value under the predetermined standards, it is sensuously difficult to eliminate the feeling of contamination due to the presence of color. Further, it is assumed that the re-use of colored effluent in production processes is rarely carried out due to concerns of any of the adverse effects to products.
The present situation is such as above, but heretofore, trials to decolorize effluent via separation of colored components have been undertaken. Specifically there is a method in which coagulants such as inorganic or polymer coagulants are added to an effluent to catch colored materials. However, colored materials such as dyes commonly exhibit high hydrophilicity, and in order to eliminate high hydrophilic materials in aqueous effluents, it has been necessary to employ a large amount of the above coagulants. Consequently, techniques to separate colored materials by decreasing the used amount of coagulants have been investigated. Specifically, a technique is disclosed in which inorganic coagulants and polymer coagulants are added to a colored effluent to eliminate colored materials (refer, for example, to Patent Document 1).
Further, a method has appeared in which by paying attention to the polarity of both polymer coagulants and colored materials, polymer coagulants having a group exhibiting a reverse polarity to that of colored materials are added, or amphoteric polymer coagulants are employed (refer, for example, to Patent Document 2).
Meanwhile, cases occur in which chelating agents (for example, polyvalent carboxylic acids or polyvalent aminocarboxylic acids) are incorporated in the effluent together with the colored materials. Chelating agents are added to used water during the production process so that product quality and productivity are enhanced. As a result, the chelating agents remain in the effluent. When inorganic coagulants are added to a colored effluent incorporating the chelating agents, colored material components once captured by inorganic coagulants (inorganic metal salts) are often re-dissolved due to effects of chelating agents, whereby it has been difficult to decolorize the colored effluent.
(Patent Document 1) Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP-A) No. 2004-154734
(Patent Document 2) JP-A No. 2004-344829